1. Field of the Invention
The invention relates to improving the rigidity of a planetary carrier of a planetary gear set having short pinions and long pinions.
2. Description of the Related Art
In a planetary gear set of an automatic transmission, generally, each gear is a helical gear for continually meshing the gears smoothly. When helical gears are used, a carrier supporting the pinions receives torsional moment based on a reaction force that occurs when the gears mesh. Therefore, if the rigidity of the planetary carrier is low, the carrier is deformed, and then the gears are not meshed appropriately. As a result, problems, such as deterioration of the durability of the gears and gear noise, occur. When a simple planetary gear is provided, a supporting span of the carrier for supporting the pinion gears is short. Therefore, it is comparatively easy to maintain the rigidity of the planetary carrier against the torsional moment. When a ravegneaux type planetary gear is provided, the axial length of the pinion is long. If the number of pinions is increased, a space for arranging bridge members axially connecting both sides of the carrier is particularly limited. Therefore, it is difficult to maintain enough cross section for maintaining rigidity against a torsional moment.
Japanese Patent No. 2852819 describes a planetary carrier formed by welding a first supporting member having a cup shape on a second supporting member having a cup shape and having a flange portion on the periphery thereof. The base wall of the first supporting member supports one end of both type of pinions, short and long, and the base wall of the second supporting member supports the other end of the short pinions. Supporting portions for the other end of the long pinions are formed by partly cutting down the surrounding wall of the second supporting member to the radial inner side, and the surrounding wall of the first supporting member is partly cut for meshing the long pinions with the ring gear.
The ravegneaux planetary carrier described above is formed by connecting both of the cup shaped supporting members, then the carrier is formed as a box shape. Therefore, the rigidity of the carrier is maintained. However, the supporting portions for the long pinions are formed by cutting down the surrounding wall, therefore, the supporting portions are supported by the flange portion at one side. Therefore, it is estimated that the rigidity for supporting the long pinions is low, and then this carrier is not suitable for a larger planetary gear set.
Further, the structure, in which the surrounding wall is partly cut for meshing the long pinions with the ring gear, is usable in case the pinion gear diameter is small. However, when the pinion gear diameter is enlarged for maintaining high capacity and high durability of the planetary gear set corresponding to high power and high speed rotation, the cut portion of the surrounding wall of the first supporting member must be large, therefore, it is difficult to maintain the rigidity of the carrier. When the diameter of the carrier is enlarged, the rigidity is maintained. However, when the planetary gear set is enlarged it is no longer lightweight and compact.
In view of the above problems associated with the prior art, an aspect of the invention is a planetary carrier which improves the durability of a planetary gear irrespective of the diameter of the pinions, supporting short pinions and long pinions.
According to an exemplary embodiment of the invention, a planetary carrier supporting plural short pinions and plural long pinions includes a first supporting wall supporting one ends of the short pinions and the long pinions, second supporting walls supporting the other ends of the short pinions, third supporting walls supporting the other ends of the long pinions, first connecting walls connecting the first supporting wall and the second supporting walls, pairs of second connecting walls facing each other, arranged on both sides of the long pinions in the rotational direction of the carrier, and connecting the second supporting walls and the third supporting walls, and third connecting walls connecting the pairs of the second connecting walls to each other on at least one of the radial inner side and the radial outer side of the long pinion.
The planetary carrier has fourth connecting walls, which extend from the second supporting walls to the third supporting walls, connecting with the third connecting walls, and forming a continuous annular wall with the third connecting walls. The planetary carrier has the annular wall formed from the third connecting walls and the fourth connecting walls, and forming a periphery wall of the planetary carrier. A spline is formed on the surface of the periphery wall.
The planetary carrier has fifth connecting walls, which connect the radial inner ends of the second supporting walls and the second connecting walls to each other.
The first connecting walls fill the spaces surrounding the peripheries of the short pinions, the peripheries of the long pinions and the peripheries of the first connecting walls which are closest to the periphery of the planetary carrier. The first supporting wall and the third supporting walls have support portions supported by other rotational members, respectively.
According to an exemplary embodiment of the invention, each pair of second connecting walls and each third connecting wall connects each second supporting wall to each third supporting wall, and forms a box structure surrounding the long pinion. Therefore, the rigidity of the carrier from each second supporting wall to each third supporting wall is improved. Generally, it is difficult to maintain the rigidity of each second supporting wall because cut down portions are formed for passing through the long pinions between the adjoining short pinions. In the invention, however, the second supporting walls are connected to the third supporting walls with the second and third connecting walls arranged along with the cut down portions so that the adjoining second supporting walls are connected to each other with the box structures formed from the second and third connecting walls and the third supporting walls. As a result, the rigidity of the second supporting wall is improved. Thus, the first connecting walls, acting as bridge portions connecting the first supporting wall and the second supporting walls to each other, can be shortened to substantially equal the axial length of the short pinion by improving the rigidity between the second supporting walls and the third supporting walls. As a result, the rigidity of the carrier as a whole is improved.
The annular wall is formed by connecting the third connecting wall and the fourth connecting wall. Therefore, the rigidity from the second supporting wall to the third supporting wall is further improved, and the rigidity of the carrier as a whole is also improved. Further, the portion of the carrier on the radial inner side of the fourth connecting wall that does not support the long pinion is formed as a space. Therefore, the carrier is lightened and the carrier rigidity is improved.
The spline is formed on the annular wall, which is continuous around the periphery of the carrier for improving the rigidity of the carrier, for using the annular wall as a hub of a clutch or a brake as a common member. Therefore, the transmission may be reduced in weight and made compact.
The second connecting wall, which connects the second supporting wall supporting the other end of the short pinion and the third supporting wall supporting the other end of the long pinion, is connected with the fifth connecting wall at the radial inner side of the carrier. Therefore, the rigidity of the carrier is further improved.
Each first connecting wall fills as much of the limited space between each short pinion and each long pinion as possible. Therefore, the rigidity of each first connecting wall, which acts a bridge member connecting the first supporting wall to the second supporting walls, is improved and the rigidity of the carrier as a whole is improved. In this case, even if the diameters of the pinions are large, the cross section of each first connecting wall can be maintained by using the space between the pinions, which are adjacent to each other. Therefore, the rigidity of the carrier can be improved without enlarging the diameter of the carrier.
Further, the first supporting wall and the third supporting walls have supported portions. Therefore, the rigidity of both supporting walls is improved, and the rigidity of the carrier is improved.